[VMM] Dirty children's filters when dirtying our filter

Fixes inability to expand folders that show up in areas they were
previously filtered in. Yay, VMM is pretty much ready.

Drop Target doesn't work and we're hiding the sort menu because it's
glitchy, but GG!~

indra/newview/llfolderviewitem.cpp

@@ -1594,6 +1594,8 @@ void LLFolderViewFolder::dirtyFilter()
 {
 	// we're a folder, so invalidate our completed generation
 	setCompletedFilterGeneration(-1, FALSE);
+	for (auto folder : mFolders) // Dirty our children's filters too, so they get updated.
+		folder->dirtyFilter();
 	LLFolderViewItem::dirtyFilter();
 }